Rails :include vs. :joins

Rails :include vs. :joins: Demystifying the Difference

Do you find yourself confused about when to use :include and :joins in Rails? 🤔 Don't worry, you're not alone! Many developers have struggled to understand the nuances between these two options. But fear not! In this blog post, we'll break it down for you and provide easy solutions to address this common issue. 💪

The Gospel on Pulling Associated Records

You may have come across the advice to use :include when pulling associated records. The reason behind this recommendation is that it avoids a whole bunch of extra queries, thanks to the magic of joining. 🎩 For example, to retrieve posts with their associated comments, you might see code like:

Post.all(:include => :comments)

Sounds good, right? But here's the kicker: when you look at the logs, there's no join happening! 😲 Instead, you see individual queries to fetch the posts and then the comments:

Post Load (3.7ms)   SELECT * FROM "posts"
Comment Load (0.2ms)   SELECT "comments.*" FROM "comments" 
                       WHERE ("comments".post_id IN (1,2,3,4)) 
                       ORDER BY created_at asc)

Uh-oh...why is :include not behaving as expected? 🤷‍♀️

The Solution: Enter :joins

To get the coveted join in your queries, you'll have to switch to using :joins instead of :include. For example:

Post.all(:joins => :comments)

And voilà! Check out the logs now:

Post Load (6.0ms)  SELECT "posts".* FROM "posts" 
                   INNER JOIN "comments" ON "posts".id = "comments".post_id

There it is! The join we were looking for! 🎉

But Why Doesn't :include Do the Join?

You might be wondering why Rails advertises :include as the way to go for joins, but it doesn't actually perform the join in this case. 🤔 The truth is, Rails is indeed aware of the performance implications of joins and chooses not to join in certain scenarios.

Performance-wise, it's not always better to do a join rather than individual queries. In fact, if you go by time spent, it might look like the two individual queries above are faster than the join. 😮

Understanding the Trade-offs

While it may be tempting to always use a join for performance reasons, it's important to weigh the trade-offs carefully. Using :include can still provide benefits, such as fetching associated records in a more memory-efficient manner. Keep in mind that loading all the associations at once can be wasteful if you only need a subset of them.

Consider the specific needs of your application and the usage patterns of the associated records. If you frequently access all the associations together on a particular screen, then using a join might be more appropriate.

Conclusion and Call-to-Action

In conclusion, the key takeaway is that :include and :joins serve different purposes in Rails. Use :include when you want to optimize memory usage and :joins when you specifically need a join in your query.

We hope this article has helped demystify the difference between :include and :joins in Rails. If you found it useful, don't forget to share it with your fellow developers! And if you have any more questions or insights on this topic, leave us a comment below. Let's keep the discussion going! 👇